U.S. Pat. Nos. 7,481,603 and 7,758,284 granted to William G. Fox (hereinafter the “Fox patents”) discloses a tensionable bolt (i.e. spiral and threaded) for use with resin nuts, and related methods, for installation in a borehole in a mine in order to support the mine from collapsing. The disclosure in the Fox patents is designed to provide support in passages of geological structures, such as mines, in an efficient, secure, and cheap way. The apparatus disclosed in the Fox patents provides a structure supporting means that is easy to use and install, does not result in protrusions from the mine support structure, has excellent tensioning/holding characteristics, has minimal tension bleed-off, and has the capability of being re-tensioned by rotation of the spiral bolt after columnar grouting. U.S. Pat. Nos. 7,481,603 and 7,758,284 are hereby incorporated by reference for all purposes.
Throughout the initial investigation of the invention disclosed in the Fox patents, manufacturing companies have found that there is not a practical method of producing the desired large quantities of bolts for the system because the bolts had to be made from standard merchant round steel bar run through cut-threading or roll-threading machines (e.g., a Landis threading machine), which produce one thread at a time by rotating the head around a stationary round bar and continuing along the shaft a defined length, usually at least 24 inches. The use of such cold-cutting and/or cold-forming processes is very slow and costly, and as such the manufacturing quantity is restricted and incapable of meeting product demand for the mining bolts at a low cost.
Bolts and screws are typically manufactured through the use of a threading process, such as machined threads, cast threads, or cold-rolled threads. In the machining process, threads are cut in a milling process on conventional or computer numerical control (“CNC”) machines. In the casting process the threads are formed by the internal surface of the casting mold. In the cold-rolling process the threads are created by rolling bar stock to form threads of the fastener through sets of two or more dies in a perpendicular orientation to the movement of one or more of the movable dies in a die set. These manufacturing processes can be costly because of the set-up and manufacturing times associated with creating specialized fasteners for various applications.
In some applications, such as the case with utilizing bolts in a mine shaft roof application, or other structural support applications, three-hundred thousand (300,000) to five-hundred thousand (500,000) bolts per month, or other amounts besides this range, may need to be manufactured to supply a single mine. This may translate into around three hundred fifty (350) plus tons of bolt stock for structural support applications in a single mine.
Different types of bolting systems and associated manufacturing processes have been implemented to either utilize standardized bolts or manufacture specialized bolts in cheaper processes that can be used in support structures. However, each invention has its own associated problems. A summary of some prior art bolts systems and processing methods are described briefly below.
U.S. Pat. No. 4,861,197 illustrates a mechanical anchor including an expansion shell and an expansion plug positioned in the shell and engaged with the end of a bar having helically extending rib segments formed on the outer surface of the bar. This bolt system is designed to employ an expansion shell as the anchoring mechanism.
U.S. Pat. No. 4,953,379 describes a method of hot-rolling full continuous threads around a bar for use in concrete reinforcing. This method is, however complicated by the mandatory employment of two sets of individually synchronized tandem mill rolls rotated at ninety (90) degrees from each other and then synchronized with each other to roll top and bottom threads, and the two side threads, thereby forming a continuous thread for the application of an anchoring or connecting member with a female thread.
U.S. Pat. No. 4,922,681 illustrates a bolt that is specifically designed to not rotate. It comprises a circular core cross-section and two rows lying opposite each other which are arranged along a helical line and form portions of a thread for screwing on an anchoring or connecting body provided with counter thread. The steps serve to improve the bond of the concrete reinforcing bar to the concrete.
U.S. Pat. No. 5,775,850 depicts particular thread forms to provide a rock bolt for use in a rock bolt system which enables the rock bolt system to have an improved performance when compared with rock bolt systems based on known rock bolts.
U.S. Pat. No. 6,886,384 B2 describes a thread form on opposing sides of a smooth bar but with the threads offset by an amount of half the thread pitch. The ribs which are so formed protrude from the bar and typically form a discontinuous thread around and along the bar. This thread form allows for the application of couplers but prohibits rotation in a set grouting medium.
There is a need for cost-effective and efficient specialized bolts that can be used in support structure applications, such as mining, tunneling, earth stabilization or construction, which can replace bolts manufactured through standard processes, but still have the same or better structural capabilities.